County outline
Where Clay County is located
Area breakdown
Land accounts for 99.1% of Clay County’s measured area and water for 0.9%. Its combined area converts to 1,483 square kilometers or approximately 366,459 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 567.238 | 1,469.14 | 363,032.3 |
| Water | 5.354 | 13.867 | 3,426.6 |
| Total | 572.592 | 1,483.006 | 366,458.9 |
How Clay County compares
By original Census land area, Clay County ranks #56 of 99 in Iowa and #1805 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.996 times the Iowa county-equivalent median of 569.6 square miles. It accounts for 1% of the combined county land area in the state.
See the complete Iowa ranking · What counts as a county equivalent?
Population and density of Clay County
The Census Bureau estimates that 16,202 people lived in Clay County on July 1, 2025. That ranks #2,091 of 3,222 county equivalents nationally and #47 of 99 in Iowa. Since the April 1, 2020 estimates base of 16,385, the population has declined by 183 (−1.1%), compared with +1.5% for Iowa as a whole.
With 567.2 square miles of land, that is 29 people per square mile (11 per km²), placing Clay County #2,046 nationally for density and #45 in Iowa. The median county equivalent has 47 people per square mile; the Iowa median is 26. Put another way, there are about 22 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 16,341 | 16,464 | 16,514 | 16,537 | 16,521 | 16,202 |
| Change | — | +123 | +50 | +23 | −16 | −319 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in Clay County
10 incorporated places lie at least partly in Clay County. Together they are home to 13,117 people (81%); the other 3,085 (19%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Spencer city, with 11,218 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Spencer cityCounty seat | 11,218 | −0.9% | 10.9 |
| Everly city | 561 | −2.6% | 1.047 |
| Royal city | 375 | −1.8% | 0.295 |
| Peterson city | 313 | −2.5% | 0.519 |
| Fostoria city | 228 | −3% | 0.406 |
| Dickens city | 145 | −2% | 0.835 |
| Webb city | 135 | −3.6% | 0.503 |
| Greenville city | 65 | −1.5% | 0.166 |
| Rossie city | 46 | −2.1% | 0.144 |
| Gillett Grove city | 31 | −3.1% | 0.222 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Clay County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Clay County is a central county of the Spencer, IA Micropolitan Statistical Area. Clay County is the area’s only county equivalent, so the micro area has the same 567.2 square miles of land. By combined land it ranks #382 of 542 micropolitan areas, and #533 by population. It belongs to the Spencer-Spirit Lake, IA Combined Statistical Area.
ZIP codes
17 ZIP Code Tabulation Areas have land in Clay County; 10 of them have most of their land inside the county, and the others mainly cover neighboring areas.
5051550565505855103351047510585130151333513385134051341513435134651357513585136451366
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering Clay County
Clay County shares a land border with 4 county equivalents. It has more land than 2 of them. The largest neighbor is Buena Vista County (574.9 mi²) and the smallest is Dickinson County (380.5 mi²). Together with its neighbors, Clay County forms a block of 2,659.6 mi² of land, of which it holds 21.3%.
| Bordering county equivalent | Land mi² | Size vs. Clay | Compare |
|---|---|---|---|
| Buena Vista County | 574.9 | about the same | Compare |
| O'Brien County | 573 | about the same | Compare |
| Palo Alto County | 563.9 | about the same | Compare |
| Dickinson County | 380.5 | 1.5× smaller | Compare |
How big is Clay County compared with U.S. states?
Clay County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.8 times as much. Iowa’s county land could hold about 98 areas the size of Clay County.
Another way to picture it: the same land area would fill a square about 23.8 miles (38.3 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about Clay County?
Clay County has more land than 1,417 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places Clay County at #1,905 nationally by total area, 100 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.
Its water share is 0.9%, compared with a national county-equivalent median of 1.2% — 0.2 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside Clay County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1804 | Adair County, Missouri | 567.3 | Compare |
| #1805 | Clay County, Iowa | 567.2 | This county |
| #1806 | Brunswick County, Virginia | 566.4 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 43.081224, -95.149875. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,469,139,455 m²; AWATER: 13,866,672 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Clay County?
Clay County, Iowa has 567.2 square miles (1,469.1 km²) of land and 5.354 square miles of water, for a total area of 572.6 square miles. It ranks #1805 of 3,222 U.S. county equivalents by land area.
Is Clay County the largest county in Iowa?
No. Clay County ranks #56 of 99 in Iowa by land area. The largest is Kossuth County, with 972.7 square miles of land.
What counties border Clay County?
Clay County shares a land border with O'Brien County, Dickinson County, Palo Alto County, and Buena Vista County.
What is the population of Clay County?
The Census Bureau estimates Clay County had 16,202 residents on July 1, 2025, ranking #2,091 of 3,222 county equivalents. That is 29 people per square mile of land.
What is the county seat of Clay County?
The county seat of Clay County is Spencer.
What cities and towns are in Clay County?
Clay County has 10 incorporated places. The most populous five are Spencer city, Everly city, Royal city, Peterson city, and Fostoria city; 3,085 residents live outside any incorporated place.
Is Clay County part of a metropolitan area?
Yes. It is a central county of the Spencer, IA Micropolitan Statistical Area.
How many ZIP codes are in Clay County?
17 ZIP Code Tabulation Areas have land in Clay County, and 10 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Clay County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.8 times as much land.
How many acres of land are in Clay County?
The land measurement converts to approximately 363,032 acres. Including water, total area is approximately 366,459 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.